Delay lock code tracking loop employing multiple timing references

Abstract

A code tracking system and method especially for use in direct sequence code division multiple access (DS-CDMA) communication systems employs multiple timing references within a chip by tracking the multiple timing references relative to the exact midpoint of the chip, then adjusting the timing references to the exact midpoint of the chip, and outputting an error tracking signal in accordance with the minimum error associated with the multiple timing references. The system performs effective code tracking with low lock-loss rate even when the noise of a receiving path interferes with detection of some of the timing references. The system uses multiple delay-locked loops for the different timing references.

1. A code tracking system for a communication system comprising a multiple timing references delay-locked loop employing N timing references, N being ≧2, said multiple timing references loop comprising:
 a pseudo-noise (PN) code generator that generates a local PN code;  
 a code tracking means for tracking an input reception signal and said local PN code output from said PN code generator in accordance with said N timing references and outputting a tracking error signal;  
 a loop filter that changes said tracking error signal to a stabilized signal; and  
 a voltage controlling oscillator that receives said stabilized signal output by said loop filter and controls a code generation timing of said PN code generator so that a code of the reception signal and said local PN code output by the PN code generator coincide, wherein 
 said code tracking means comprises: 
 N timing reference tracking units that track each of said N timing references T i  and output a decision signal D i  for each timing reference T i , where 1≦i≦N; and  
 a code tracking decision unit that receives said decision signals D i , finds a minimal tracking error from said decision signals D i  and outputs a selected decision signal D i  associated with one of said timing references associated with said minimal tracking error, said selected decision signal D i  comprising said tracking error signal.  
 
 
 
   
   
     2. The code tracking system according to  claim 1 , wherein said timing reference tracking units comprise:
 a bulk delay element for outputting an early reception code advanced relative to the local PN code generated from said PN code generator by a predetermined early time;  
 a bulk delay element for outputting a late PN code delayed relative to the local PN code generated from said PN code generator by a predetermined late time and;  
 a first correlator for correlating the reception signal with the signal of said early PN code and outputting a correlation signal of early code;  
 a second correlator for correlating the reception signal with the signal of said late PN code and outputting a correlation signal of late code;  
 a tracking decision unit for receiving and subtracting the correlation signals of early code and of late code and outputting a decision signal comprising at least one of a re-acquisition signal and a tracking error signal;  
 a bulk delay element for delaying said decision signal a predetermined adjustment time and outputting the delayed decision signal to said code tracking decision unit.  
 
   
   
     3. A code tracking system according to  claim 2 , wherein said first and second correlators are correlate-and-dump circuits. 
   
   
     4. A code tracking system according to  claim 1 , wherein said multiple timing references delay-locked loop is for use in a direct-sequence code division multiple access communication system. 
   
   
     5. A method of code tracking in a communication system, said method employing N timing references, N being ≧2, said method comprising:
 (a) generating a local PN code;  
 (b) tracking an input reception signal and said local PN code in accordance with said N timing references and outputting a tracking error signal;  
 (c) changing said tracking error signal to a stabilized signal; and  
 (d) employing said stabilized signal to control a code generation timing of said local PN code so that a code of the reception signal and said local PN code coincide, wherein 
 step (b) comprises tracking each of said timing references and outputting decision signals associated with said timing references, finding a minimal tracking error from said decision signals and outputting a selected one of said decision signals associated with one of said timing references associated with said minimal tracking error as said tracking error signal.  
 
 
   
   
     6. A method according to  claim 5 , wherein said communication system is a direct-sequence code division multiple access communication system.